Process and apparatus for supplying alumina

ABSTRACT

PROCESS AND APPARATUS FOR SUPPLYING ALUMINA TO AN IGNEOUS ELECTROLYSIS TANK CONTAINING MOLTEN MATERIAL AND HAVING A CRUST ON THE SURFACE THEREON WHEREIN THE CRUST IS PIERCED ALONG AT LEAST ONE SERIES OF POINTS ALONG ONE AXIS OF THE TANK, A SOURCE OF ALUMINA IS MOVED CONTINUOUSLY ALONG THE PIERCED ZONE WHILE FEEDING ALUMINA TO THE OPENINGS FORMED IN THE CRUST, PIERCING THE CRUST ALONG AT LEAST ONE SERIES ALONG ANOTHER AXIS OF THE TANK AND CONTINUOUSLY MOVING A SOURCE OF ALUMINA ALONG THE SECOND PIERCED ZONE WHILE CONTINUOUSLY FEEDING ALUMINA TO THE OPENINGS FORMED IN THE CRUST.

BEST AVAILABLE COPY July 25, 1912 v D. DUCLAUX ET 3,679,555

I PROCESS AND APPARATUS FOR SUPPLYING ALUMINA F. led April 16. 1970 v Sheets-Sheet. 2

ll; 31 311 S61 33 O a 312 i 5s 1am 333 34 BEST AVAILABLE COPY. July 25, 1972 D. DUCLAUX ET AL 3,679,555

PROCESS AND APPARATUS FOR SUPPLYING ALUMINA Filed April 16. 1970 7 Sheets-Sheet 5 Fig. 3

353T AVAILABLE COPY July 1972 D. DUCLAUX ETAL 3,679,555

PROCESS AND APPARATUS FOR SUPPLYING ALUMINA Filed April 16. 1970 7 Sheets-Sheet 4 Fig. 1.

Brs'r AVAILABLE COPY y 1972 D. DUCVLAUX ETAL 3,679,555

PROCESS AND APPARATUS FOR SUPPLYING ALUMINA Filed April 16. 1970 7 Sheets-Sheet 5 Fig.6

Fig.7

BEST AVAILABLE GOPY PROCESS AND APPARATUS FOR SUPPLYING ALUMINA Filed April 16. 1970 July 25, 1972 D, DUCLAUX ET AL '7 Sheets-Sheet BEST AVAILABLE COPY July 25,, 1972 D. DUCLAUX ET AL 3,67 ,555

PROCESS AND APPARATUS FOR SUPPLYING ALUMINA Filed April 16. 1970 7 Sheets-Sheet 7 United States Patent "ice 3,679,555 PROCESS AND APPARATUS FOR SUPPLYING ALUMINA Daniel Duclaux, Lille, Jean-Pierre Givry, Ville-dAvray, and Jacky Pointud, Marseille, France, assignors to Compagnie Pechiney et Electrification and Charpente, Levage, fractional part interest to each Filed Apr. 16, 1970, Ser. No. 29,034 Claims priority, appliggitigsgrance, Apr. 16, 1969,

Int. Cl. C22d 3/02, 3/12 US. Cl. 204-67 14 Claims ABSTRACT OF THE DISCLOSURE Process and apparatus for supplying alumina to an igneous electrolysis tank containing molten material and having a crust on the surface thereon wherein the crust is pierced along at least one series of points along one axis of the tank, a source of alumina is moved continuously along the pierced zone while feeding alumina to the openings formed in the crust, piercing the crust along at least one series along another axis of the tank and continuously moving a source of alumina along the second pierced zone while continuously feeding alumina to the openings formed in the crust.

The present invention relates to a process and apparatus for supplying alumina to igneous electrolysis tanks in the preparation of aluminum.

Supplying alumina to the surface of an electrolysis bath generally involves two operations. In the first, the crust which forms on the surface of the molten bath is either continuously or intermittently broken, and then alumina, preferably in powdered form, is fed to the openings formed in the crust in either a continuous or intermittent fashion. The quantity of alumina dissolved in the bath should be carefully controlled because the alumina content of the bath should remain within the range of 19% by weight. When the amount of alumina falls below the minimum of 1%, there is produced in the bath a polarization of the anode, commonly referred to as the anode effect. If the quantity of alumina in the bath exceed about 9%, the alumina fed to the bath is no longer dissolved, and the resulting alumina powder present in the bath is deposited upon the cathode, thereby significantly increasing the internal resistance of the tank and otherwise disturbing its operation.

It is known that alumina powder can be supplied to igneous electrolysis tanks in the preparation of alumina by piercing the crust at a given number of points and then feeding measured quanities of alumina to one or more of the points at which the crust is pierced. This operation can be repeated until all of the portion of the path has been supplied with alumina. Heretofore, these two operations have been been carried out by means of a single machine which is adapted to being moved in front of the tanks treated and which includes a piercing hammer and an alumina container having a definite capacity which, in turn, is supplied by hopper which is also carried by the machine.

Examples of machines of the type described may be found in French Pat. No. 1,245,598 and No. 1,526,766.

The process and appartus as described in the foregoing French patents have the advantage of facilitating the feeding of alumina to a freshly punctured or pierced surface before the elctrolysis bath has sufiicient time to reform the crust on the surface thereof. However, while the process and apparatus as described in the foregoing French patents represent a definite improvement, they neverthe- 3,679,555 Patented July 25, 1972 less provide an irregular distribution of alumina in the bath whereby small heaps or piles of the powdered alumina are formed.

Another disadvantage of the processes and apparatus described by the foregoing patents stem from the fact that they are capable of operating on only one side of the tank with the other side being treated subsequently. As a result, alumina cannot be suplied to the tank in a symmetrical manner, thereby further increasing the lack of homogeneity.

It is also known that the crust of a bath may be pierced or broken continuously by means of a cutting head formed of a wheel fixed to the end of an oscillating shaft, which operates to break the crust by piercing it at one point and then to cut a continuous groove as it is advanced through the tank while simultaneously feeding alumina from a hopper mounted on the apparatus.

The process as described has the advantage of providing a more regulated supply of alumina, but is not without disadvantages. In the first place, the rate of feed of alumina is not constant because it depends upon the height of the alumina bed in the hopper. In the second place, by virtue of the method in which the crust is pierced or broken, there is frequently insuflicient force available for piercing a very hard crust, which can only be pierced by a conventional pneumatic piercing hammer. In addition, when greater force is available for piercing the crust, the use of such greater force frequently results in the total collapse of the crust between the edge of the anode system and the talus or slope when the crust is soft, which, in turn, increases the risk of increasing the alumina con centration in the bath to the point of saturation of the bath with the result that alumina becomes deposited on the cathode. Moreover, width of the wheel is generally such that all puncturing at the top of the tanks is not possible, and the process requires a very heavy machine which is expensive to manufacture and operate.

It is accordingly an object of the present invention to provide a method and apparatus for supplying alumina to an igneous electrolysis tank in the preparation of aluminum which overcomes the aforementioned disadvantages.

It is a more specific object of the present invention to provide a method and apparatus for supplying alumina to an igneous electrolysis tank containing molten aluminum and having crust thereon which facilitates a measured and regularly distributed supply of alumina over the surface of the bath and the maintenance of a regular layer or bed of alumina on the bath.

These and other objects and advantages of the invention will appear hereinafter more clearly, and, for purposes of illustration, but not of limitation, embodiments of the invention are shown in the accompanying drawings in which:

FIG. 1 is a schematic diagram of a top view of one portion of a tank which can be supplied with alumina according to the process and apparatus of the present invention, indicating the distribution of points along which the crust is pierced;

FIG. 2 is a side elevation view of apparatus for piercing the crust and supplying alumina embodying the features of the invention;

FIG. 3 is a view as seen from a tank, of the upper portion of FIG. 2 to illustrate the positioning of the jacks and balancing means;

FIG. 4 is a view in axial section of a constant flow alumina distributor;

FIG. 5 is a sectional view of the distributor shown in FIG. 4 taken along the lines a-a of FIG. 4;

FIG. 6 is a view parallel to the axis of the tanks being supplied of an embodiment of a machine for supplying a series of transversely positioned tanks making use of the apparatus described in FIGS. 2-5;

FIG. 7 is a view of the machine shown in FIG. 6 taken along an axis perpendicular to the axis being supplied;

FIG. 8 is a view of the side of the apparatus adjacent to the wall of the building illustrating more clearly the apparatus described in FIG. 7;

FIG. 9 illustrates an automatically compressed air supply suitable for use with the device of the present invention;

FIG. 10 is a view of the device shown in FIG. 7 illustrating position detectors and the excitation blades; and

FIG. 11 is a view of the position detectors and their excitation blades of the hammer and distributor assembly.

In accordance with the process of the present invention, the solid crust which covers the molten bath in the preparation of aluminum from alumina is first pierced or punctured and then alumina, preferably in the form of alumina powder is fed to the surface of the bath along the pierced or punctured zone. Each operation of piercing and feeding alumina is effected simultaneously along two points which are symmetrically in relation to one axis of the vertical plane of the tank, and preferably the longitudinal axial plane of the tank. In the first step, the first head of the tank is pierced or punctured along substantially regularly spaced points, and then alumina is continuously fed onto this head. In the second step, the crust is punctured or pierced along substantially regularly spaced points, first along the longitudinal side of the bath and then along the second head. In the third step, alumina is continuously fed to the zone pierced during the second step, with the feeding of alumina being effected in a manner such that the delivery of the alumina to the surface of the bath is constant. According to a preferred process embodying the features of the present invention, the piercing means of the means for supplying alumina to the bath are displaced relative to the bath simultaneously wherein the piercing of the crust is effected during travel of the piercing means in one direction relative to the bath, while alumina is supplied to the bath during the return travel of the piercing hammer and alumina supply means.

- tion parallel to the longitudinal axis of the tank and which carries on either side of the longitudinal axis of the tank two identical assemblies comprising a piercing or puncturing hammer, an alumina hopper and means for supply ing alumina from the hopper to the bath. The hopper is preferably connected to the means for supplying alumina to the bath, such as an alumina pouring pipe by means of a constant pouring alumina distributor and at least one rotor formed by blades mounted for rotation on a shaft. The shaft is driven by means having a substantially constant speed. The alumina distributor is mounted in a. pivotal fashion on two pairs of substantially parallel levers and which may be pivoted at their other end on a horizontal frame fixed to the hopper. The front pair of levers, positioned on the tank side are longerthan the other pair of levers.

The piercing or puncturing hammer is pivotally mounted onto other substantially parallel pairs of levers which, in turn, can be pivoted at their other end on the distributor. In this lever system, the lower pair of levers are longer than the upper pair. The assembly comprises a first jack adapted to act upon the inclination of the levers carrying the piercing or puncturing hammer. Both assemblies, including the first two jacks, the second two jacks, the two hammers and the two distributors of the two assemblies are connected in parallel.

' Referring now to the drawings, there is shown a diagrammatical view of a tank containing molten aluminum comprising a casing 1000 and an anode system 1001. The function of the apparatus and the process of the present invention will be described hereinafter with respect to the operation on one side of the longitudinal axial plane 1002 of the tank. However, it will be understood that the apparatus operates symmetrically on both sides of the longitudinal axial plane 1002 in both the piercing or puncturing operations and the feeding operations.

The process of the present invention generally involves a first step wherein the crust of the tank is punctured or pierced along the points 101 to 104 which are preferably substantially equally spaced. Thereafter, alumina is poured onto the head defined by these tanks with the pouring operation being effected along a horizontal line substantially perpendicular to the plane of symmetry 1002 of the tank. In the second step, the crust of the tank is pierced or punctured along a series of substantially regularly spaced points, first along the longitudinal side of the bath along a line at points 105, 107 117, 119, or along several parallel, and preferably 2 lines, represented by points 105-119 and points 106-120, and then along the second head at points 121-124. In the last step, the apparatus is displaced at a constant speed along the zone punctured or pierced during the second step and the alumina is constantly fed to the openings formed in the crust at a constant rate.

While one of the assemblies is effecting the piercing operation 101-124, the other device, which is identical and symmetrical, is simultaneously effecting the same operation at points 101' to 124', which, as indicated above, are symmetrical with points 101 to 124 relative to the axis symmetry 1002.

The pouring or feeding of alumina to the bath normally is effected at a constant rate because the pouring pipe, which is carried along with the piercing hammer, is displaced at a constant speed. However, it will be understood that the rate of displacement of the pouring pipe need not be constant in which case the feeding operation can be effected at varying speeds with the result that the rate of delivery per unit of surface bath remains constant.

The feeding or pouring of alumina can be effected during return travel of the piercing hammer-alumina feed assembly, after an outward travel during which the crust of the tank is punctured or pierced by the piercing hammer.

The apparatus of the present invention is preferably mounted on a moveable support member which is moveable parallel to the axis of the tank, and may be a bridge or gantry. 'Ihe moveable support member carries two assemblies of the type shown in FIG. 2 and FIG. 3, each of which comprise a hopper 1 forming an alumina reservoir from which is suspended a piercing and pouring assembly for an adjustable delivery which is dependent upon the height of the alumina in hopper 1. The latter is connected by a flexible pipe 11 to a constant delivery alumina distributor 2.

Suspended from the hopper 1, by means of four insulating joints 30, is an assembly comprising two horizontal beams 31 and 32, each of which is equipped with a bearing 311 and 321, respectively. Each bearing carries a horizontal shaft 312 and 322' respectively, supporting a horizontal frame 33 formed by two strongly braced girders 331 and 332. This frame is provided with a stirrup memher 333, on which is pivoted a stabilizing spring 334. for the suspended mass, pivoted at the other end on the iron girder 31. This spring insures that the latter only oscillates beyond a predetermined stress.

The distributor 2 is suspended from the horizontal frame 33 by two pairs of substantially parallel levers which are pivoted at their ends and in identical manner in pairs, the front pair 34 on the tank side being longer and the rear pair 35 being shorter. The distributor is thus able to undergo a reciprocatory movement according to the arrow 10 in a direction substantially parallel to the girder 33, that is to say, perpendicular to the longitudinal plane of symmetry 1002 of the tank. Pivoted in pairs on the shafts 361 and 371 fixed to the distributor 2 are four parallel levers, the upper and shorter pair bearing the reference 36 and the lower and longer pair the reference 37. These levers are similarly pivoted on two pivots 362 and 372 integral with a puncturing or piercing hammer 4 fitted with a puncturing or piercing tool 41. The length of the levers of the pair 36 and the length of the levers of the pair 37 may be determined graphically, by trial and error, so that the hammer 4 is slightly inclined relatively to the vertical in its top position; hammer 4 is only slightly inclined as it descends so as to be able to slide along the slip formed by the portion of the electrolysis bath solidified along lateral walls of the casing 1000 of the tank.

The reciprocatory displacement of the distributor is assured by a mechanical, hydraulic or pneumatic jack -51, pivoted at one of its ends on a shaft 511 integral with the frame 33 and at its other end on a shaft 512 integral with the levers 34. When the jack is mechanical, it is preferably provided with a resilient means permitting the tool 41 of the hammer 4 to slide along the slope. The downward displacement of the piercing hammer 4 is assured by a jack 52 pivoted at one of its ends on a shaft 521 fast with the levers 36 and at its other end on a. shaft 522 fast with a support 38 fixed to the distributor 2. The levers of the pair 34 are longer than those of the pair 35, the lengths being determined graphically by trial and error so that, under the action of the jack 51, the jack 52 remains ready, and the end of the tool 41 describes, during the piercing of the head of the tank, substantially a horizontal straight path, or, preferably, a curve having a point of inflection at a horizontal tangent toward the middle of the head-piercing zone.

The balancing of the advancing movement of the puncturing hammer 4 is achieved by a balancing device 56 which operates to place the oscillating assembly in substantially indifferent equilibrium. This balancing device, which can be a spring, a pneumatic shock absorber or a counter-weight, is pivoted on the one hand on a pivot 561 fixed on the frame 33 and on the other hand on a pivot 562 mounted on a lever 391. This latter forms part of an assembly 39 comprising two levers 391 and 392 pivoted together at 393, the lever 391 being pivoted at its other end at 394 on the frame 33 and the lever 392 being pivoted at its free end on the support 38 at 395. The balancing device is in a neutral position, that is to say, at rest, when the oscillating system is in a middle position, in which position the eifect of gravity is zero. The balancing is desirable to permit sufiiciently progressive deaccelerations of the oscillatory movement to thereby insure suflicient precision in bringing the tool into the working position.

The alumina distributor 2 comprises a distributor body 21 and at least one rotor 22 formed by blades 221 to 224 rotatably mounted on a shaft 24 which is rotated by a motor and reducing gear assembly or a hydraulic motor 241, the speed of which can be regulated, for example, by using a variable speed reduction gear, or by interposition of adjustable valve means on the supply circuit of the hydraulic motor. It is also possible, by means of a clutch, to connect the shaft 24 to the motor insuring the displacement of the whole arrangement along the tank. It is obvious that an electro-mechanical arrangement is also suitable.

In the embodiment which is shown in FIGS. 4 and 5, the distributor is in two stages, the body 21 being divided into two superimposed compartments by a metal plate 221 substantially perpendicular to the shaft 24. Openings 212 formed in this plate permit alumina to pass from the upper stage to the lower stage.

The upper compartment houses the first rotor 24 comprising the four blades 221 to 224, while the lower compartment houses a second rotor 23 comprising the blades 231 to 234. The eight blades are fixed to the same shaft 24 driven by the motor 241 described above.

The distributor body 21 comprises a supply pipe 213 to the inlet of the first stage and a discharge pipe 215 at the outlet from the second stage. A dust-extraction pipe 214 may also be provided on the entry side of the first stage when the alumina is transported in fluidized form. Finally, deflectors 216 for the first stage and 217 for the second stage improve the efliciency of the apparatus.

The discharge pipe 215 is connected to an alumina pouring pipe 12 discharging near and slightly behind the puncturing or piercing hammer so that the position of the jack 51 corresponding to the pouring is identical with a puncturing position.

In the operation of the apparatus the assembly is first brought to the head of the tank to be punctured or pierced and supplied after having brought the two jacks 51 and 52 into the re-entry position. The jack 51 is then open so as to bring the hammer 4 above the first point to be punctured 101-displacement in the direction of the arrow 10and then the jack 62 is maintained in the opening direction, so that the tool 41 of the hammer reaches a position flush with the alumina covering the tank, and the hammer is set in operation while continuing to act on the jack 52 in the same direction. When the point 101 is pierced, the hammer 4 is stopped and the jack 52 is returned to the re-entry position. The jack 51 is then maintained in the opening direction until the hammer 4 arrives above the second point 102 which is to be pie'rced and then piercing is carried out as above. This operation is continued until the piercing of the head of the tank is completed.

After piercing the last point 104, that is to say, the point closest to the longitudinal axial plane 1002 of the tank, the hammer 4 is returned to the raised position by re-entry of the jack 52, the rod of the jack 51 is re-entered at a speed corresponding to the longitudinal displacement of the apparatus at the time of pouring as described below in connection with the third step, and simultaneously the distributor 2 is set in operation. The movement of the lever and the rotation of the distributor are stopped when the jack is once again in the position corresponding to the piercing of the first point 101 produced in the head.

In carrying out the second step, the whole of the apparatus is displaced parallel to the axis of the tank, so as to bring the hammer 4 above the following point 105 which is to be pierced and the piercing is effected as above. The lengthwise piercing can be eflfected along a single line or along a plurality of lines, preferably two. In the first case where the piercing is effect along a single line the jack 51 does not move, and the points 107 117, 119, 121 are successively pierced by displacement of the whole assembly. In the second case, after puncturing the point 105, the jack 51 is operated and a point 106 in the second line, which already contains the point 102, is pierced. The jack 51 is then returned to its previous position, the assembly is displaced to the right of the following point 107 and the operation is continued.

The piercing in a lengthwise direction is continued by continuing the operation up to the last point 119 and possibly 120, whereafter the piercing of the second head is carried out, at the points 121 to 124, as explained above in connection with the first head.

The third step is then carried out. The hammer 4 is brought to the raised position by re-entry of the jack 52, the distributor 2 is set in operation and the jack rod 51 is caused to re-enter at a speed equal to that defined in connection with the top pouring. The jack 51 is stopped when it is once again in the position of the first pierced point of the head during the second step, and then the assembly is set in continuous operation at a constant speed and in a direction opposite to the displacement effected during the piercing. When the head of the tank already supplied during the first step is reached, the rotation of the distributor 2 is stopped. As a result, the entire zone pierced during the second step has thus been covered with alumina. Finally, the assembly is displaced so as to bring it in position at the head of the tank to be re-supplied.

It is to be noted that, with each puncturing or piercing operation, the alumina deposited during the preceding operation is caused to descend into the bath. Consequently, one is not absolutely master of the quantity of alumina mixed with the bath at each operation, but, on the average, this quantity is equal to the quantity poured on each operation, if only the number and the distribution of the puncturing points have been correctly established.

, It is advantageous for the jack 52 and the hammer 4 to be connected in parallel from a pneumatic (or hydraulic) point of view because in supplying the circuit, the jack 52 is first operated, which operation requires only a small pressure; the hammer is only set in operation when the resistance of the crust stops the opening of the jack.

To obtain the same result, it is also possible to provide the tool 41 of the hammer with a microcontact setting the hammer in operation as soon as the tool is forced into the body of the hammer 4 under the effect of a resistance appearing at the end of the tool.

The method of supply as described insures a rate of feed of alumina which is more regular and more homogeneous than the old methods with the result that the efliciency of the tanks is improved.

The aforementioned apparatus describes the equipment of an automatic machine designed with a view to supplying a series of tanks disposed crosswise.

The moveable support mentioned in the general description of the apparatus is preferably adapted to the arrangement of the building to be equipped. The supplying of tanks-disposed crosswise generally requires double movement, that is movement perpendicular to the longitudinal axis of the tanks, in traveling from one tank to the other and parallel to the axis during the supply operation. [In the example as described and as shown in FIGS. 6 and 7, movement is effected by a half-gantry straddling the tanks of the series, while the second movement is effected by a carriage 6 which is displaceable on rails fixed on the half-gantry with the carriage carrying two assemblies identical with that shown in FIGS. 2 to 5, disposed symmetrically in relation to the vertical plane of symmetry 700 of the half-gantry, which plane, during a supply operation, is brought into coincidence with the longitudinal plane of symmetry 1002 of the tank which is involved.

The half-gantry 7 comprises a vertical column 71 resting on the ground by means of wheels 72, fitted with solid or pneumatic tires. This column or pillar supports at its upper end a horizontal cross-member 74 formed by four bearers 741 to 744 braced by plates 745 to 749. The cross-member 74 supports a track 73 comprising two rails 731 and 732. At its end opposite to that which is supported by the vertical pillar 71, the cross-member 74 is equipped with brackets 75 supporting two bogies 750 and 751, each comprising at least one roller 752 and 753 adapted to roll on a roller tarck 758 fixed to the wall 81 of the building. At its end adjacent the bogies 750-751, the cross-member carries a compressed air reservoir 760. The distance which separates the two bogies 750 and 751 should be sutficient to provide high stability and great precision in the guiding movement. This latter is further increased by rollers 754-755 having vertical shafts, acting on the lateral faces of the roller track 758.

The carriage 6 comprises a frame 61 formed by strongly ,braced I-section or U-section girders. This frame carries four flanged wheels 621 to 624. The alumina hoppers 1 are fixed rigidly to this frame by girders 63.

In contrast to the prior apparatus, the half-gantry 7 need not comprise either a supply pipe for compressed air or electric cables which are unwound or wound up as it is moved in front of the tanks of the series to be supplied. The electric current is preferably supplied by means of trolleys and with the use of wipers, while the 8 supply of compressed air is obtained by means of automatic supply devices disposed on the wall 81 of the building.

The horizontal cross-member 74 carries a compressed air nozzle 76 which insures a supply of compressed air to the reservoir 760 every time that the half-gantry 7 is in the operating position above a tank. For this purpose, the wall 81 carries a compressed air conduit 82 connected, opposite each tank, to a frusto-conical end 821 by means of an automatic valve 822. Arranged on the horizontal cross-member is a female bell-shaped member 761 adapted to be tightly engaged around the frusto-conical end 821. This bell is connected to the reservoir 760 by a flexible tube 762; it is carried by a support member 763 whereby the free end is pivoted on the end of a lever 764 and the other end, representing the fixed point, is pivoted at a point on the horizontal cross-member 74 and an intermediate point is pivoted on the end of the rod of a jack 53. When this jack is in a position in which the rod is in the re-entry position, the bell 761 is retracted relative to the end 821 and no connection is established. When the jack 53 is in a position with the rod extended, the bell 761 is in the advance position and it engages around the end 821 when alignment is obtained. A spring 766 holds the bell while permitting a slight lateral displacement. A non-return valve 767 prevents the air of the reservoir from escaping through the bell when the latter is not engaged on the end. The engagement of the bell around the end controls the opening of the valve 822.

The electric current supply is effected by means of three trolleys 831 to 833 insulated from the building by an insulator 830 and from one another by insulators 836 and 837. Two other trolleys 834 and 835, insulated by the insulators 838 and 839, serve for the transmission of urgency signals as will be hereinafter explained. The bracket 75 carries wipers 771 to 775, which insure the pick-up of current by contact with the respective trolleys 831 to 835.

The hoppers 1 can be filled with alumina at loading sta- I tions 84 disposed at regular intervals along the wall 81.

Each station comprises two identical devices, one for each hopper, disposed symmetrically in relation to the longitudinal plane of symmetry of a tank whereby loading can be carried out with the machine in position for supplying the tank, without the half-gantry having to be displaced. A loading station is preferably for one tank in ten to one tank in thirty, these figures being given by way of example.

Each of the devices which form the station 84 comprises a fixed alumina supply tube 841 connected at one end to a large-capacity reservoir (not shown) and at the other end to a fixed connection head 842 connected by a flexible tube 843 to a pivoted joint 844 connected at the other end, by means of a tube 845, to a moveable head 846, whereby the alumina can. flow into the hopper 1. A jack 54, connected at one end to the fixed head 842 and at the other end to the tube 845, permits the latter to rock about the pivot joint 844. The moveable head 846 forms a female element capable of receiving a corresponding male element 13 carried by the hopper 1.

The apparatus of the invention can be provided with a sequential control assembly, in which each step in the supplying operation is efiected by one or more position detectors transmitting the fact that all the members are in the desired position so that the action can be initiated.

The half-gantry 7 is equipped with position detectors, namely, detectors 781 and 782 for the precise positioning of the half-gantry, detector 783 for the commencement of the zone, which is excited when the machine is in its rest position, for example, at the end of the building, detector 784 for the tanks situated opposite and alumina supply station, zone termination detector 785 excited if the machine goes beyond the last of the tanks served by it, and detectors 786 and 787 for counting the tanks. Facing each tank, the wall 81 carries a small metal bar 851 adapted to actuate the detectors 781 and 782 which has a length sufiicient to permit the simultaneous excitation of two detectors 786 and 787, and finally a detector 860 of the position of the machine, the latter detector being adapted to be excited by a plate 790 carried by the machine. Facing the rest position of the machine, the wall 81 also carries a plate 853 capable of exciting the detector 783 and, beyond the last tank to be treated by the machine, a plate 852 adapted to excite detector 785.

As shown in FIG. 7, the horizontal cross-member 74 carries five position detectors, namely, detector 791, which is excited when the carriage 6 is in the waiting position, at the end of the half-gantry and on the side opposite to that of the wall 81, detector 792, which is excited when the carriage is in the position for commencing the puncturing operation, which is also the head puncturing position, facing the points 101 to 104, detector 793, which is excited when the carriage is in the position completing the puncturing, which is also the head puncturing position on the wall side 81, facing the points 121 to 124, and finally, detector 794, which is excited when the carriage is in the position where it is appropriate to stop the alumina distributors 2 at the end of the pouring operation. In addition, a detector 795 is provided which is excited when the carriage is in the position for recharging the hoppers, that is to say, in the position which is illustrated in FIG. 7. The carriage 6 carries a plate 651 for the excitation of all these detectors.

The position of the assembly formed by the puncturing hammer 4 and the pouring pipe 12 on the tank or retracted from the tank is shown in FIG. by position detectors mounted on a support 339 and adapted to be excited by a plate 340 integral with the levers 34. These detectors are: a detector 341 corresponding to the retracted position of the assembly relative to the tank, a detector 342 corresponding to the lengthwise piercing before the anodes, plus a certain variable number of detectors corresponding to positions of the hammer 4 increasingly advanced towards the axis of the tank when it is desirable that the longitudinal puncturing of the anodes be made along two lines including one detector 343 corresponding to the second line, the detector 342 corresponding to the more outward first line. A certain number of detectors may also be provided which are used only with the head piercing, for example, two detectors 344 and 345. It is possible to make the position of these detectors adjustable except for the detector 341, there being no reason for this to be moved. The figure shows a gap 346 which enables these detectors to be made moveable.

The raised or rest position of the puncturing hammer 4, the position at the end of piercing or puncturing a hole in the lower position is determined by two position detectors: a raised position detector 381 and a lowered position detector 382, both fixed to the body 21 of the alumina distributor. These detectors can be excited by a plate 380 mounted on the suspension levers 36 of the hammer.

The half-gantry 7 and the carriage 6 are such actuated by a two-speed motor, for example, a fast speed and a slow speed.

The operation of the machine and the manner in which it is used are hereinafter explained.

At rest, the machine is in the waiting position, for example, at one end of the electrolysis building which is being served. The zone commencing detector 783 is then excited by the plate 853 carried by the wall 81 facing the rest position. The carriage 6 is also in its rest position at the end of the horizontal cross-member 74 near the vertical column 71 whereby the plate 651 excites the position detector 791. Finally, the hammer 4 is in the raised position, so that the detector 381 is excited by the plate 380. The simultaneous existence of these conditions permits the machine to be started at high speed in the direction of the tanks. The detector 783, the purpose of which is to stop the machine in the rest position and to prevent its departure in a direction opposite to that of the tanks, is no longer excited, but this has no effect on the operation.

When the machine approaches the first tank to be supplied, the bar 851 excites detector 781 or 782 which it first encounters. In the following explanation, it is assumed that bar 851 contacts detector 781. The excitation of detector 781 causes the machine to be brought to slow speed, with movement of the machine being stopped when both of these detectors are simultaneously excited. Thus, when the bar 851, without ceasing to act on the detector 781, excites the detector 782, the movement of the machine stops. The machine can pass slightly beyond the corresponding position when the bar 851 excites detector 782 but ceases to act on 781 with the result that the machine is restarted at slow speed but in the opposite direction, until both of the detectors are excited and the machine is stopped.

The simultaneous excitation of the detectors 791, 381, 781, and 782 results in the outward movement of the rod of jack 53, and the connection of the automatic air pipe 821-761. As the detector 341 is excited by the plate 340, because distributor 2 and hammer 4 assembly is in the rear position, the carriage 6 is set in movement, first at high speed, and then, under the effect of a delay device, at slow speed, until the excitation of the detector 792 causes the cessation of movement. The hammer assembly is then in position for the puncturing or piercing operation, that is to say, opposite the line of the points 101 to 104. The excitation of the detector 782 also initiates the puncturing operation in that the two jacks 51 of the two symmetrical hammer assemblies are actuated in the direction of the outward movement of the rod, until excitation of the detector 342 by the plate 340 whereby jack 51 is stopped. The hammer descends until the tool 41 encounters the crust, which results in a resistance which in turn leads to an increase in the common supply pressure of the jack 52 and hammer 4 and the initiation of the movement of the latter, which punctures the point 101. The hammer acts on the crust and any reduction in resistance to the descent is shown by an additional outward movement of the rod of the jack 52. The hammer thus descends as fast as it breaks the crust, until the plate 380 excites the detector 382, which stops the supply of fluid to the jack 52 in the sense of re-entry of the rod and the return of the hammer towards the top position. When the hammer does not meet any more resistance, the supply pressure drops again to the value necessary for the operation of the jack 52, whereby the puncturing by the hammer is stopped. When the plate 380 excites the detector 381, the supply of fluid to the hammer and the jack 52 is terminated. At the same time, jack 51 is actuated by pressure until the detector 343 is excited and this, while stopping the jack 51 starts up the ack 52 and the hammer in order to puncture the point 102, as explained above in connection with point 101. The operation continues until the detector 345 is excited and the last point 104 is punctured, resulting in the retraction of the hammer until excitation of the detector 342 and resulting in the starting up of the distributor 2. The alumina is poured on to the punctured or pierced zone through the pipe 12 during the retraction of the suspended assembly 2-4. The excitation of detector 342 stops the dlstributor 2. It is to be noted that, if the hammer is incapable of breaking the crust, a delay device stops its action after a predetermined time, without waiting until the detector 382 is excited. It should also be noted that each movement or step is possible only if the two symmetrical apparatus mounted on the carriage and acting simultaneously on either side of the plane of longitudinal symmetry of the tank have completed the preceding movements.

With detector 342 excited and the hammer in the raised position (detector 381 excited), the carriage starts again at slow speed for a time determined by a timing mechanism, as a function of the spacing of the points to be pierced. The stopping of the carriage determines the piercing of the point 105. If a piercing operation along 1 1 two lines is provided, the completion of the piercing operation at point 105 stops the supply of fluid to the ack 51 until the detector 343 is excited, which in turn stops the jack and determines the piercing of the point 186 which, in its turn, causes the feeding of the relay 51 in the direction for re-entry of the rod until excitation of the detector 342, which in turn initiates the movement of the carriage for the predetermined period as defined above. The piercing operation is continued until the excitation of the detector 793 by the plate 651 causes a second piercing operation, identical with the foregoing, with pouring of the alumina during the return of the suspended assembly When the detector 342 is excited, with the alumina having been poured on to the head on the wall side 81 of the tank, jack 51 is stopped and remains in the corresponding position, while the motor of the carnage is started up again at high speed. As the dlstributor 2 continues to function, the alumina is poured in front of the anodes over the full length of the tank. When the detector 794 is excited by the plate 651, the distributor is stopped. The position of the detector is chosen so that the pouring operation continues as far as the end of the tank, by,

emptying the pipe 12. However, the movement of the carriage is continued until the plate 791 1s excited, which causes, on the one hand, the stoppage of its movement in the position of FIG. 6 and the re-entry of the ack 51 until excitation of the detector 341, and on the other hand the re-entry of the rod of the jack 53 and the uncoupling of the compressed air supply device.

Consequently, the conditions necessary for the movement of the half-gantry 7 are satisfied: the suspended distributor-hammer assembly 2-4 is retracted, the carriage is at the end, on the wall side 81, of the horizontal crossmember 72 and the air supply is uncoupled. The halfgantry restarts at high speed as far as the following tank, and the same operations start again.

When the zone terminating detector 785 is excited by the plate 852 after puncturing the last tank, the machine returns to its inoperative position until the timing mechanism causes it to start for a new supply operation.

The alumina filling points of the hoppers 1 are in the supply position when the half-gantry is aligned with one of the tanks, provided for this purpose, of the series to be supplied. A plate 854 is disposed facing each of the tanks concerned. When the detector 784 is excited by one of these plates, the carriage, after the piercing operation and before supplying the tank, is displaced toward the end on the wall side 81 of the horizontal cross-member, until the detector 795 is excited, which determines the functioning of the jack 54, the connection of the charging bell 846 with the frusto-conical end 13, and the feeding of a supply chute. Each hopper 1 has a level detector (not shown), the excitation of which causes the stopping of the supply to the chute, the re-entry of the jack rod 54, the starting in reverse of the carriage and the supply to the tank.

It is possible still further to improve this assembly by using a tank counter which counts the tanks when the detectors 786 and 787 are excited in the order 786-787 by the plate 856 and deducts them when these detectors are excited in the reverse order 787-786. This counter can have added thereto a manual indicator of tanks to be treated, permitting the recording of the tanks to be supplied, excluding those which do not have to be supplied. A comparator then compares the reading of the counter with that of the indicator, and the machine is only stopped if the number recorded by the counter is shown by the indicator. However, it is stopped in front of the tanks equipped with a device supplying the hoppers 1 with alumina, but without proceeding to the puncturing operation and the supply of the tank, if the latter is not shown on the manual indicator.

-It is possible to equip the machine in such a way that it responds to urgent calls, for example, a tank suffering from anode effect. An emergency installation connected to the building and no longer, as before, to the half-gantry 7, receives the indication of the voltage at the terminals of each tank. When this voltage exceeds a given value, the number of the corresponding tank is recorded in a memory. The machine continues its work on the tank which it is in the course of supplying, but when it has completed this work and it is ready to start again for supplying the following tank, it receives an emergency signal through the trolleys 834 and 835. By means of the detector 860, the emergency device receives the indication of the number of the treated tank. By comparison of the number of the tank or tanks suffering from anode effect, it establishes the direction of displacement to be given to the machine in order to proceed to these tanks, the forward travel having preference over rearward travel in the case of tanks under anode effect situated on either side of the tank being normally supplied. The apparatus is set in operation at high speed until the number of the tank given by the detector 860 is identical with one of the numbers in the memory. This tank is then treated as explained above, and the machine only takes up its normal supply procedure after having treated all the tanks of which the memory has recorded the number. Normal working is recommended at the point where it has been interrupted by the emergency calls by means of a memory recording, at the moment of these calls, of the number of the last tank supplied under normal working conditions.

The electrical circuits for the control means as mentioned above are not described herein, but are generally similar to those set forth in French Pat. No. 1,526,766.

It will be apparent from the foregoing that we have provided a new and improved apparatus and process for supplying alumina to an electrolysis tank for use in the preparation of aluminum. The process and apparatus of the present invention have the advantage that they supply measured quantity of alumina to the bath which can be regularly distributed over the surface of the bath to progici; for more uniform conditions within the electrolysis It will be understood that various changes and modifications can be made in the details of procedure, construction and use without departing from the spirit of the invention, especially as defined in the following claims.

What is claimed is:

1. A process for supplying alumina to a igneous electrolysis tank containing molten material and having a crust on the surface thereof comprising the steps of (l) piercing the crust along a series of points in a direction substantially perpendicular to the longitudinal axis of symmetry on each side of the axis of symmetry, moving a source of alumina along the series of points in a direction opposite to the direction in which the piercings are made to feed alumina onto the crust, (2) piercing the crust along at least one series of points in a direction sub stantially parallel to the axis of symmetry on each side of the axis of symmetry, (3) piercing a second series of points in a direction substantially perpendicular to the axis of symmetry on each side of the axis of symmetry and moving a source of alumina along the series of points of (2) and (3) in a direction opposite to the direction in which the piercings are made to feed alumina onto the crust, with the ratio of the rate of alumina feed to the surface area covered by the alumina source being constant.

2. A process as defined in claim 1 wherein the points of each series are regularly spaced each from the other.

3. A process as defined in claim 1 wherein the crust is pierced along a plurality of series of points in (2), each of said series defining a straight line parallel to the axis of symmetry.

4. Apparatus for supplying alumina .to an igneous electrolysis cell containing molten material and having a crust on the surface thereof, which includes a support member which is movable relative to the tank along the axis of symmetry thereof, two crust piercing assemblies,

each of said assemblies being mounted on said support member on each side of the axis of symmetry of the tank and each of said assemblies comprising a piercing hammer, said piercing hammer being mounted on a support for oscillatory motion on two pairs of levers, jack means operatively connected to one of the levers to actuate the piercing hammer whereby the head of the hammer travels through a substantially straight path to pierce the crust of the cell, and means to supply alumina to the tank.

5. Apparatus as defined in claim 4 wherein said means to supply alumina to said tank includes pipe means, a distributor to supply alumina at a constant rate to said pipe means and an alumina hopper to supply alumina to said distributor.

6. Apparatus as defined in claim 5 wherein said pipe means is positioned to deposit alumina adjacent to said piercing hammer.

7. Apparatus as defined in claim 5 wherein said distributor includes a body, at least one rotor mounted for rotation on a shaft, and means for rotating said shaft at a constant speed.

8. Apparatus as defined in claim 4 wherein each of said crust piercing assemblies are connected in parallel.

9. Apparatus as defined in claim 4 wherein said means for actuating said hammer includes balancing means to control the oscillatory movement of said hammer.

10. Apparatus as defined in claim 4 wherein said moveable support member is supported by a half-gantry on one end and by a rail at the other end, said gantry being movable on at least one wheel and said rail being carried by a wall.

11. Apparatus as defined in claim 4 wherein said apparatus includes automatic control means to control movement of said support member, actuation of said hammer and the feed of the alumina.

12. Apparatus as defined in claim 11 wherein said control means prevent each operation of the apparatus from taking place until the preceding operation is terminated.

13. Apparatus as defined in claim 11 wherein said control means includes means responsive to a disruption in the operation of one tank whereby said control means interrupts the operation of supplying a plurality of tanks after the apparatus has completed the cycle of operation of the tank being supplied at the time the disruption occurs.

14. Apparatus as defined in claim 13 wherein said automatic control means includes memory means to resume the operation of supplying a plurality of tanks after the tank in which the disruption has occurred is supplied.

References Cited UNITED STATES PATENTS 3,192,140 6/1965 Zorzenoni 204247 XR 3,551,308 12/1970 Capitane et al. 204246 XR 3,567,206 3/ 1970 Heggstad et a1. 204245 XR FOREIGN PATENTS 1,495,653 8/ 1967 France 204245 1,376,385 9/1964 France 204245 248,133 7/1966 Austria 204245 204,595 1/1968 USSR. 1 204245 JOHN H. MACK, Primary Examiner D. R. VALENTINE, Assistant Examiner U.S. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,679,555 Dated July 25, 1972 Daniel Duclaux et al It is certified that errors appear in the above identified patent and that said Letters Patent are hereby corrected as shown below.

Column 3, line 67, before levers insert first pair of levers and a second jack adapted to act upon the inclination of the Signed and sealed this 30th day of January 1973.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

